I have a bunch of the 1.5-2 gallon hex aquariums that Walmart used to sell... they were very easy to work with. I didn't use the UGF, just did a total clean-out every few days.
There wasn't the problem with distortion, either. The clear lid set easily inside the black rim, and there was a light fixture on top that held either an incandescent bulb or the small CF bulb, which I preferred.
I probably have 8 of them in my closet, since I don't have that many bettas anymore, just one.
Hmm...that reminds me.... I need to go clean out his tank!